Scaffold having a shaped strut and methods for shaping scaffold struts

Abstract

A scaffold strut is shaped to improve hemocompatibility. After laser cutting, the scaffold is placed on a work piece and its struts are shaped by flame polishing or brushing. The abluminal surfaces and luminal surfaces can have corners rounded. The strut can have a sloped surface on its luminal side without reducing strut thickness needed for strength.

The invention claimed is: 
     
       1. A medical device, comprising:
 a balloon catheter including a balloon located at a distal end and a distal tip; and 
 a polymer scaffold crimped to the balloon, the scaffold having a pattern of shaped struts, wherein a shaped strut has a leading edge, a trailing edge, a luminal surface facing a surface of the balloon and an abluminal surface facing away from the balloon surface; 
 wherein the shaped strut is, in respect to a cross-section of the strut, asymmetric about each of two orthogonal axes passing through a centroid of the strut cross-section; and 
 wherein the shaped strut further includes a linear or non-linear taper from the leading to the trailing edge thereof such that a strut thickness at the trailing edge is less than the strut thickness at the leading edge; and 
 wherein the shaped strut leading edge is located a first distance from the distal tip, the shaped strut trailing edge is located a second distance from the distal tip, and the first distance is greater than the second distance. 
 
     
     
       2. The medical device of  claim 1 , wherein the strut thickness at the trailing edge is between about 20% and 60% of the strut thickness at the leading edge. 
     
     
       3. The medical device of  claim 2 , wherein the shaped struts have an aspect ratio (AR) of strut width to strut thickness between 1 and 4. 
     
     
       4. The medical device of  claim 3 , wherein a maximum thickness of the strut is between 80 microns and 120 microns. 
     
     
       5. The medical device of  claim 4 , wherein the scaffold is substantially or completely made from a blend of polylactide (PLA) and a PLA and polycaprolactone (PCL) random copolymer (e.g., 5-30% PCL) and the blended PLA-PCL combination has between about 1% to 8% by weight PCL. 
     
     
       6. The medical device of  claim 4 , wherein the scaffold is substantially or completely made from poly(L-lactide) PLLA. 
     
     
       7. The medical device of  claim 1 , wherein the scaffold is orientated on the balloon so that the shaped strut leading edge is upstream of the shaped strut trailing edge when the scaffold is being implanted at a treatment site. 
     
     
       8. The medical device of  claim 1 , wherein the shaped strut comprises a radius of curvature for a corner of the luminal surface and a corner of the abluminal surface, and wherein the radius of curvature at the luminal surface corner is about 3 times higher than the radius of curvature at the abluminal surface corner. 
     
     
       9. A medical device, comprising:
 a balloon catheter including a balloon, a distal end and a distal tip; and 
 a scaffold crimped to the balloon, wherein the scaffold is made from a tube and the tube is substantially or completely made from a blend of polylactide (PLA) and a PLA and polycaprolactone (PCL) random copolymer (e.g., 5-30% PCL) and the blended PLA-PCL combination has between about 1% to 8% by weight PCL; 
 the scaffold including a shaped strut, wherein the shaped strut has a leading edge, a trailing edge, a luminal surface facing a surface of the balloon and an abluminal surface facing away from the balloon surface; 
 wherein a cross-section of the shaped strut is asymmetric about each of two orthogonal axes passing through a centroid of the strut cross-section, such that a strut thickness at the trailing edge is between 30% and 80% of the strut thickness at the leading edge; 
 wherein the shaped strut leading edge is located a first distance from the distal tip, the shaped strut trailing edge is located a second distance from the distal tip, and the first distance is greater than the second distance. 
 
     
     
       10. The medical device of  claim 9 , wherein the tube from which the scaffold was made has a wall thickness, and wherein the strut thickness at the leading edge is between 70% to 95% of the wall thickness. 
     
     
       11. The medical device of  claim 9 , wherein the tube from which the scaffold was made has a wall thickness, and wherein the strut thickness at the trailing edge is between 30% and 60% of the wall thickness. 
     
     
       12. The medical device of  claim 9 , wherein a corner of the trailing edge located on the luminal surface of the shaped strut has a higher slope than a corner of the leading edge located on the abluminal surface of the shaped strut. 
     
     
       13. A medical device, comprising:
 a balloon catheter including a balloon, a distal end and a distal tip; and 
 a scaffold crimped to the balloon, wherein the scaffold is made from a tube having a wall thickness, and the tube is substantially or completely made from a blend of polylactide (PLA) and a PLA and polycaprolactone (PCL) random copolymer (e.g., 5-30% PCL) and the blended PLA-PCL combination has between about 1% to 8% by weight PCL; and 
 the scaffold further comprising ring elements formed by struts connected at strut junctions, the struts including shaped struts located at the strut junctions, wherein a shaped strut comprises a leading edge, a trailing edge, a luminal surface facing a surface of the balloon and an abluminal surface facing away from the balloon surface, the shaped strut further comprising:
 a cross-section asymmetric about each of two orthogonal axes passing through a centroid of the cross-section, 
 a leading edge thickness between 70% to 95% of the wall thickness, 
 a trailing edge thickness between 30% and 60% of the wall thickness, 
 
 a radius of curvature for a corner of a luminal surface is about 4 times higher than a radius of curvature for a corner of an abluminal surface; and wherein the shaped strut leading edge is located a first distance from the distal tip, the shaped strut trailing edge is located a second distance from the distal tip, and the first diameter is greater than the second distance.